Process for preparing a fuel additive and the additive

ABSTRACT

The invention relates to a method for manufacturing a fuel additive and to the additive. It relates particularly to a lubricant additive that is highly suitable for use as an additive in connection with diesel engines. According to the method, saturated fatty acids with a high melting point are separated by cooling from a fatty-acid mixture, the said fraction of fatty acids with a high melting point being esterified and/or aminated to form a mixture of more than three esters and/or amines and the mixture thus obtained being re-mixed with that part of the original fatty-acid mixture from which the fatty acids with a high melting point were separated and the necessary amount of this last-mentioned mixture being mixed with fuel to form a lubricant. The separation of the saturated fatty acids with a high melting point takes place by passing the mixture through a cooling heat-transfer surface, to which the fatty acids adhere, and by removing the fatty acids from the surface by raising its temperature.

[0001] The present invention relates to a method for manufacturing a fuel additive and the additive. The invention particularly relates to a lubricating additive, which is especially suitable for use as an additive used with diesel engines.

[0002] The continual increase in the prices of fuels, particularly fuels for combustion engines, and the tightening of environmental regulations have lead to numerous proposed and actual improvements in both engines and in fuels.

[0003] In automotive engines, engines based on the Diesel cycle are gaining ground over petrol engines, due to the greater thermal efficiency of diesel engines. In addition to their existing efficiency, based on a high compression ratio, their operation has been further improved by using fuel injection into the combustion chamber.

[0004] At the same time as environmental demands have led to a great reduction in the sulphur content of these fuels, polyaromatic and other closed-chain compounds, which as such have excellent lubricating properties for high-pressure fuel-injection equipment, have been removed from the fuel along with the sulphur.

[0005] Fatty acids have proven to be good additives for fuel, particularly diesel fuel. However, fatty acids have the well-known drawback that they crystallize or that substances such as stearic acid and arachid acid crystallize easily out of them, in other words, fatty acids as such are not suitable for very cold conditions. The esters of these acids also easily crystallize out of, for instance, olive oil.

[0006] U.S. Pat. No. 6,129,772 discloses a fuel additive, manufactured from saturated fatty acids and from oligomeric fatty acids, in which tertiary amines are used to prevent crystallization. The patent emphasizes especially that mixtures of different saturated fatty acids are not used, but gives no reasons for this.

[0007] U.S. Pat. No. 5,578,090 discloses a fuel and a fuel additive, which is characterized in that it is composed of the esters of fatty acids, some of which are glycerine esters and some are triglycerides.

[0008] WO 94/17160 discloses a fuel additive, comprising a fatty acid, which is esterified using alcohol containing one or several carbons.

[0009] EP 826765 discloses a corresponding diesel-fuel additive, which is a fatty acid and a partial ester of polyol, for example, glycerine and an ester of monocarboxylic acid, 75-200 ppm of which is added to middle distillates.

[0010] U.S. Pat. No. 3,765,850 discloses an additive obtained by permitting dicarboxylic acid to react with polyamides.

[0011] U.S. Pat. No. 6,156,082 discloses that it is preferable if a fuel lubricant is not esterified, as the lubricity will then suffer. However, this patent describes partial esterification with diethylene glycol and an organic acid anhydride, which results in excellent lubricity.

[0012] U.S. Pat. No. 6,194,361 discloses that a usable lubricant can be obtained from the distilled fatty acids of tall oil by allowing the fatty acid of tall oil to react with diethanolamine and then allowing the fatty acid to react with aminoethylpiperazidine after the previous reaction. This compound is used, among other things, for lubricating oil wells, both with oil and as a water emulsion.

[0013] U.S. Pat. No. 6,197,731 discloses that a suitable lubricant for two-stroke engine fuel can be obtained by esterifying polyols with polycarboxylic acids.

[0014] JP 08092581 discloses how the —OH group of castor oil can be esterfied with a saturated monovalent fatty acid to obtain a lubricant that will operate at very low temperatures.

[0015] U.S. Pat. No. 6,086,645 discloses how a fuel additive can be advantageously obtained by manufacturing amides of carboxylic acids for this purpose from oleic acid and/or linolenic acid.

[0016] U.S. Pat. No. 5,882,364 discloses a corresponding fuel additive comprising the esters of an unsaturated fatty acid and a polyvalent alcohol, two grades of which are mixed together in the same mixture.

[0017] U.S. Pat. No. 6,203,584 discloses a fuel additive comprising esters of polybasic carboxlic acid and polyoxyamine and a mixture of carboxylic acid and an ester of polyvalent alcohol, which acts with them.

[0018] U.S. Pat. No. 5,997,593 discloses a fuel lubricant comprising the reaction product of carboxylic acid and an amine, in which the said amine is guanidine, amino guanidine, urea, or thiourea.

[0019] U.S. Pat. No. 6,051,039 discloses a diesel fuel additive, which is obtained from an amine of dicarboxylic acid, which is an amine derivative of succinic acid or phtalic acid and their mixture, as well as of an NR₃ amine, in which R contains 6-24 carbons. The mixture is added to diesel fuel in a concentration of at least 1000 ppm.

[0020] U.S. Pat. No. 5,556,972 discloses how fats can be fractionated by crystallizing a stearin ester fraction from an oleic acid fraction in two stages and removing the said stearin fat fraction by filtration. This reduces the cloud point of the fat. The process is carried out by countercurrent crystallization, which thus reduces, for example, the congealing point of margarine.

[0021] U.S. Pat. No. 5,952,518 discloses a method, by means of which fatty acids with a high melting point can be removed from other fatty acids. In this case, the assistance of an emulsifier is used, the mixture is cooled, and the saturated fatty acids are removed from the mixture by crystallization. Esters of a polyvalent alcohol and a fatty acid are used as the emulsifier. The fatty acids are hydrolyzed rapeseed or soya oils.

[0022] The fatty acids of tall oil, as stated in many patents, act well as fuel lubricants in combustion engines, as do their alcohol esters with alcohols, and the amines of fatty acids. However, the fatty acids as such would be the best lubricants.

[0023] Saturated fatty acids and their derivatives are stated to act particularly well as lubricants.

[0024] Particularly stearic acids and their salts have been used throughout history as good lubricants.

[0025] The present invention is intended to create a lubricant based on fatty acids and a method for manufacturing it for use as a fuel additive to improve lubrication. This is achieved in the manner stated to be characteristic in the accompanying Claims.

[0026] According to this invention, the question is how to very advantageously eliminate the said problems and drawbacks, when using compositions of tall oil and other fatty acids as an internal lubricant in fuel at low temperatures.

[0027] According to the invention, the fatty-acid composition is given a cold-treatment, preferably using such a heat exchanger, in which the fatty-acid composition is circulated, until a sufficient share of the amount of the fatty acids has crystallized on the heat-transfer surfaces of the heat exchanger being used and essentially only unsaturated fatty acids flow out of the composition.

[0028] Typically, saturated fatty acids crystallize out of a tall oil fatty-acid composition already at a temperature of 10° C., most of the stearic acid crystallizing already at a temperature of 5° C. The rest will also crystallize at the temperature range 5-10° C. Normally, the crystallization process is slow and can take many days when the said fatty-acid mixtures stand in a vessel. This is due to the low diffusion coefficient and the high viscosity in cold conditions. When the composition is pumped through a heat-transfer surface, the low diffusivity is compensated by the mass transfer caused by the flow as such.

[0029] Now that the saturated fatty acids have been made to solidify on a heat-transfer surface, they can be removed from the surface by separately heating it. Thus a new fatty-acid composition is obtained, which has a substantially greater amount than before of saturated fatty acids, typically palmitinic acid, stearic acid, and arachinic acid. Typically these total, for example, 2-4% by weight of a tall oil fatty-acid composition. The melting point of unsaturated fatty acids is much lower than that of saturated fatty acids, but the lubricating properties of saturated fatty acids are, in turn, better, which is a generally known fact.

[0030] The separated saturated fatty acids can be preferably esterified, aminated, and permitted to react with enhancing cyclic compounds, such as lactams, oxazolidines, and similar. It is generally known that the melting point, solidifying point, or the pour point known in technology of each mixture occurs at a lower temperature, the more the mixture contains related but not identical compounds. Further, it is possible to envisage and claim that the more a mixture contains such compounds (in this case fatty-acid compounds), which form steric inhibitions to crystallization, branchings, branches, pendant groups, etc., then the lower will be the temperature at which the mixture will solidify, or at which crystals or a separate phase of some compound will precipitate from it.

[0031] According to the present invention, at least most of the saturated fatty acids are separated from a fatty-acid composition by crystallization at a low temperature, and are made to react with an alcohol mixture, preferably with waste, i.e. fusel oil, obtained from the manufacture of alcohol, which contains many alcohols with a high boiling point, so that a mixture of many esters will be obtained directly. Some of the saturated fatty acids are, in turn, made to react with amines, particularly with N,N-dimethyl or N,N-diethyl amines, when an excellent solvent and a low melting point for the said solvent will be obtained.

[0032] Part of the saturated fatty-acids separated from the composition can be advantageously made to react at an increased temperature and in the presence of an acid catalyst with lactams, preferably with capric lactam. This reaction must not include a large number of unsaturated fatty acids, because polymerization takes place easily and a solid phase with a high melting point will be obtained (+50° C.).

[0033] Before the reaction with amines, preferably N,N-dimethyl or diethyl amines, a small amount of an oleic acid-linoleic acid mixture can be added to the mixture, thus providing an advantageous solvent for other reactions.

[0034] Thus, according to the present invention, saturated fatty acids are separated from a fatty-acid mixture by crystallizing them, preferably on cold heat-transfer surfaces, the mixture of essentially saturated fatty acid being separated by heating the said heat-transfer surface and given an esterifying treatment in the presence of an acid catalyst, preferably using an alcohol mixture containing many different alcohols and/or a part of the said mixture of saturated fatty acids being allowed to react with amines, preferably with N,N-diamine and/or a part being permitted to react with lactams, preferably with capric lactam, at an increased temperature, and at least one of these reaction mixtures being remixed with the original mixture made from essentially unsaturated fatty acids.

[0035] The aforementioned method has advantages, including the fact that only part of the fatty acids, generally 2-5%, must be treated and the best fatty acids, even though modified, can be used for lubrication. If the separate and modified fraction is multi-modified, the solidification point of this fraction will be at a lower temperature than if it had been esterified or aminated using only a single reagent.

[0036] The reaction product of capric lactam and fatty acids is like vaseline, provided the reaction of the product is stopped at a suitably early stage, for example, 30 min/150° C. If the product is kept hot, for example, for 2 hours, a relatively solid product will result, which will not longer optimally suit the purpose referred to here. The catalyst used is an acid catalyst, para-toluenesulphonic acid, Lewis acid, or concentrated cation exchange resin or sulphuric acid, which must, however, be washed out. Normal Lewis acids, such as AlCl₃ are very suitable for this purpose.

[0037] When aminating fatty acids, there is reason to use advantageously N,N-dimethyl or ethyl fatty-acid amines, as they do not form hydrogen bridges with each other and thus remain liquid at room temperature.

[0038] When esterifying fatty acids, one of the cheapest raw materials is an alcohol mixture, which in the alcohol industry goes by the name of fusel oil. If this is used in esterifying, many esters of fatty acids and acids will be obtained at one time, while a low solidification point for the reaction mixture will also be obtained.

[0039] The product thus obtained is typically mixed with diesel fuel to form a 0.01-0.04% mixture.

EXAMPLE 1

[0040] A tall oil-fatty acid mixture, which according to analysis contained palmitinic acid 0.4%, stearic acid 1.1%, and arachid acid 0.4%, was cooled to and kept cooled at a temperature of +5.5° C., until no further sediment was deposited from it. In this case, the solution was filtered, the filtration producing about 50 ml of mixture from a litre of the original composition. The solidification point of the sediment was 35° C. The composition of this mixture contained 8.3% of stearic acid (1.1% in the original mixture). It is obvious that filtration in a laboratory will not produce such good results as crystallization on cold heat-transfer surfaces, because a large amount of the other acids present in the mixture will remain between the crystals of the sedimented stearic acid.

EXAMPLE 2

[0041] 29 g of the stearic-acid concentrate obtained in Example 1 and 10 g of capric lactam were allowed to react with each other with a small amount of AlCl₃ acting as a catalyst while being mixed for 2.5 hours, during which time the melting point of 40° C. had dropped to a value of 35° C. The result was a viscous golden-brown liquid, which was like vaseline at room temperature. Later, a part of it precipitated, which solidified when the mixture was kept for 2 days at a temperature of 60° C., in other words, it had continued to polymerize.

EXAMPLE 3

[0042] Fusel oil traditionally contains salts that can be removed prior to use in esterification, for example, by distillation. However, in this case the salts were removed in another way; i.e. the fusel oil was cooled to a temperature of −18° C., when about one-fifth of the water precipitated as a salt phase, which was removed together with the salts, the remainder being used as follows.

[0043] Thus, stearic acid was esterified using an alcohol mixture, of so-called fusel oil, which was obtained from the waste of the distillation of ethanol. The composition of the fusel oil was: propanol 3 w-%, isobutanol 24 w-%, 2-methyl-1-butanol 12 w-%, 3-methyl-1-butanol 37 w-%, ethanol 8 w-%, water 14 w-% ja solids in the form of salts 0.5 g/litre, which were removed according to the above procedure.

[0044] 10 g stearic acid (sp 67-69° C.) was mixed with 80 ml of the fusel oil described above and a small amount (2 drops) of sulphuric acid was added. The mixture was first heated, while being mixed, at a temperature of 94.2° C. for 2 hours, after which the surplus alcohols were distilled out, when the remainder of the alcohols also began to leave at a temperature of 145° C. The mixture was washed with water to remove the acid residues. The remaining ester mixture was still entirely fluid and clear at a temperature of +14.5° C. It will be obvious to one versed in the art that if the said esterification has been carried out using the stearic-acid concentrate referred to previously, a clearly smaller amount of processing could have been achieved, as the relative amount of saturated fatty acids would have been greater.

EXAMPLE 4

[0045] 30 g of the fatty-acid mixture of Example 1, concentrated in relation to stearic acid, was allowed to react with 13.6 g of di-N-butyl amine, using a drop of sulphuric acid as a catalyst, at a temperature of 120° C. for 4 hours while mixing, a pale orange liquid being obtained, which was highly fluid at a temperature of +7° C. A clear increase in the viscosity of the liquid began only at a temperature of +2° C. while it began to form a solid phase only at a temperature of −1° C.

EXAMPLE 5

[0046] The solution remaining in Example 2, which was a light brown liquid, with a viscosity clearly greater than that of fatty acids, was mixed with the filtrate of Example 1, in which there was thus a large amount of unsaturated fatty acids, together with the amine esters of stearic acid manufactured in Example 4, in which case the amount corresponded to the amount of the ‘stearic-acid fraction’ removed by crystallization. The fatty-acid mixture thus created was allowed to stand for several days at a temperature of +2° C., during which time no sediment appeared in it, even though the same original product (Example 1, +5° C.) continued to crystallize significantly in the same conditions.

EXAMPLE 6

[0047] The same amount that had been removed of both the alcohol-esterfied stearic acid and the mixture of saturated fatty acids esterified using di-N-butyl amine (the sediment that had been filtered from the original solution at a temperature of +2° C.), were added to the fatty-acid mixture of Example 1, from which the saturated fatty acids that had crystallized at a low temperature had been filtered out.

[0048] This solution was kept at a temperature of −1° C. for 7 days. No sediment was deposited from it, nor did it become cloudy. At the same time, further sediment began to settle, at the same temperature, from the alkali solution from which sediment had been removed at a temperature of +2° C.

EXAMPLE 7

[0049] 28 g of the sediment of saturated fatty acids separated according to Example 1 was melted and 10 g of capric lactam and 2 drops of AlCl₃ solution were added to it and the reaction was allowed to proceed while mixing at a temperature of 150° C. for 60 minutes. The result was a vaseline-like product with a solidification point of 35° C., the solidification point of the original liquid being 40° C. An amount of this product corresponding to the stearic acid and arachid acid together with the fusel-oil esters was mixed with the filtrate according to Example 1, so that there was as much of each reaction product calculated as stearic acid, as had been removed from it. After being allowed to stand for 3 days at a temperature of −1° C., an amount of needle-like crystals, which were only just visible to the naked eye, was deposited from the product. When the crystals were melted and the product was allowed to stand for 4 days, at a temperature of +5° C., no further sediment or crystals were formed.

[0050] When a mixture of esters of di-N-butyl amine stearic acid, arachid acid, and palmitinic acid of 0.5 ml per 100 ml was added to this mixture, a fatty-acid solution was created, from which nothing further was deposited at −1° C. The product was also noted to have an easily emulsifying effect on water. 

1. A method for manufacturing fatty-acid compounds for use as a lubricant fuel additive, characterized in that saturated fatty acids with a high melting point are separated from a fatty-acid mixture by cooling, the fraction of the fatty acids with a high melting point is esterfied and/or aminated to form a mixture of more than three esters and/or amines and the mixture thus created is re-mixed with that part of the original fatty-acid mixture, from which the fatty acids with a high melting point were separated, and mixed with the necessary amount of this last-mentioned mixture to form a fuel lubricant.
 2. A method according to claim 1, characterized in that the fatty acids with a high melting point are separate from the fatty-acid mixture by passing the mixture through a cooling heat-transfer surface and that the fatty acids adhering to the cold surface are removed by raising its temperature.
 3. A method according to claim 1, characterized in that the fraction of saturated fatty acids with a high melting point is esterified using a mixture of several alcohols.
 4. A method according to claim 3, characterized in that the esterification takes place using fusel oil.
 5. A method according to claim 4, characterized in that the esterification takes place using a fusel oil in which there is water, the salts dissolved in which being removed by cooling the said fusel oil to a temperature of less than 0° C., particularly to a temperature of −10-−25° C. and removing the separated water phase.
 6. A method according to claims 4, characterized in that the fusel oil is distilled prior to the esterification treatment.
 7. A method according to claim 1, characterized in that the fraction of fatty acids with a high melting point is aminated, particularly using diamines or amino-alcohols and/or lactarns.
 8. A method according to claim 7, characterized in that the amination takes place at a temperature of 130-150° C. and in the presence of an acid catalyst while mixing for at least 1 hour.
 9. A method according to claim 7, characterized in that the amination takes place using N,N-dialkylamines.
 10. A method according to any of the above claims, characterized in that the saturated fatty acids are treated by both esterification and amination, either together or separately, and that the products obtained are mixed with the unsaturated fatty acids that remain from the fatty-acid mixture, from which the saturated fatty acids were separated.
 11. A lubricant fuel additive comprising fatty-acid compounds, characterized in that it includes esterified and/or aminated saturated fatty acids with a high melting point and unsaturated fatty acids with a low melting point.
 12. An additive according to claim 11, characterized in that the additive contains esters of saturated fatty acids with a high melting point together with several alcohols.
 13. An additive according to claim 11, characterized in that the additive is formed of essentially the fatty acids of tall oil, the saturated fatty acids of which are esterified/aminated. 